That of, of all of the in-school factors that exist, the teacher quality is the factor that has the most impact on student achievement levels.

那就是，在所有存在的校内因素中，教师质量是对学生成绩水平影响最大的因素。

Here's another example. That of, of all of the in-school factors that exist, the teacher quality is the factor that  has the most impact on student achievement levels.

这是另一个例子。也就是说，在所有存在的校内因素中，教师素质是对学生成绩水平影响最大的因素。